The present invention relates to a cryogenic precooler used during the initial cool down operation of a superconductive magnet.
Superconducting magnets now in use operate at very low temperatures. To start up these magnets, the sensible heat needs to be extracted from the magnet to cool them from room temperature to cryogenic temperatures. Due to the large mass of the magnets used for whole body magnetic resonance imaging, the amount of energy to be withdrawn is substantial. A slow cooling of the magnet using the cryocooler, which is typically sized for steady state operation, can take many days. A fast cooling of the magnet can, however, result in thermal stresses which could structurally damage the magnet.
Presently precooling is accomplished in magnets having a cryocooler for cooling the shield by passing cryogenic liquid through a tube which is loosely wound around the magnet shield. This requires additional plumbing as well as additional physical space.
It is an object of the present invention to provide a precooler which can quickly cool down a superconductive magnet at a controlled rate to avoid excessive thermal stresses.
It is another object of the present invention to provide a precooler which does not require additional plumbing or additional space in the superconductive magnet winding or magnet cryostat.
It is a further object of the present invention to provide a precooler which is completely removable from the superconductive magnet and does not add to the cost of the magnet.
It is a still further object of the present invention to provide a precooler which uses an existing multistage cryocooler interface.